/*
This file is part of the iText (R) project.
Copyright (c) 1998-2025 Apryse Group NV
Authors: Apryse Software.

This program is offered under a commercial and under the AGPL license.
For commercial licensing, contact us at https://itextpdf.com/sales.  For AGPL licensing, see below.

AGPL licensing:
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
using System.IO;
using iText.Kernel.Pdf;

namespace iText.Kernel.Pdf.Filters {
    /// <summary>Handles RunLengthDecode filter.</summary>
    public class RunLengthDecodeFilter : MemoryLimitsAwareFilter {
        /// <summary><inheritDoc/></summary>
        public override byte[] Decode(byte[] b, PdfName filterName, PdfObject decodeParams, PdfDictionary streamDictionary
            ) {
            MemoryStream outputStream = EnableMemoryLimitsAwareHandler(streamDictionary);
            byte dupCount;
            for (int i = 0; i < b.Length; i++) {
                dupCount = b[i];
                if (dupCount == (byte)0x80) {
                    // this is implicit end of data
                    break;
                }
                if ((dupCount & 0x80) == 0) {
                    int bytesToCopy = dupCount + 1;
                    outputStream.Write(b, i + 1, bytesToCopy);
                    i += bytesToCopy;
                }
                else {
                    // make dupcount copies of the next byte
                    i++;
                    for (int j = 0; j < 257 - (dupCount & 0xff); j++) {
                        outputStream.Write(b[i]);
                    }
                }
            }
            return outputStream.ToArray();
        }
    }
}
